This isn't the first time we've reported on the long-rumored high-performance BMW X5 M. In fact, we showed you spy shots on July 25, 2007, August 31, 2007, and again on October 16, 2007. So, here we go again...

Rumors about powerplants thrive, but our best guess indicates BMW will not be dropping the M5/M6's 5.0-liter V-10 into the upcoming range-topping X5. The V-10 is a silky screamer, but torque is what's needed to motivate the X5's mass (the V-10 is rated at 500 hp, but just 383 lb-ft of torque). Instead, it is much more likely (and cost-effective) that BMW will fit a modified version of the twin-turbo 4.4-liter V-8 found under the hood of the new BMW X6. In stock form, that engine pumps out 400 hp and 450 lb-ft of torque. Tweak the engine mapping while increasing the boost, and 500 hp and 500+ lb-ft of torque isn't unimaginable. That is plenty of juice to fend off the Porsche Cayenne Turbo (500 hp/516 lb-ft) and the Mercedes-Benz ML63 AMG (503 hp/465 lb-ft).

The spy shots show an X5 with a custom front bumper fabricated to maximize cooling airflow. The fog lamps are gone, instead replaced with intakes that appear to be hiding oil coolers in the front fenders (similar to the unit found in the right front fender of the twin-turbo BMW 335i). The quad tailpipes are identical to the ones found on the prototype in October. However, unlike the images last Fall, this black prototype is wearing winter rubber--it should, as it is sitting on snow.

[Source: The Auto Channel]